The present invention relates generally to high performance polishing systems for use in modifying a substrate by Hertzian indentation, fluid-based wear and/or any similar-type non-microgrinding mechanism; the polishing systems of the present invention are particularly well suited for use in the manufacture of semiconductor devices or the like. More particularly, the compositions and methods useful in the method of the present invention are directed to polishing systems comprising an aqueous based polishing fluid and a polishing pad; the polishing pads of the present invention comprise a polishing layer having two separate phases: a high modulus phase and a low modulus phase.
Definition of Terms
1. Polishing. xe2x80x9cPolishingxe2x80x9d is intended to mean chemical-mechanical polishing (as opposed to micro-grinding) and is intended to include planarization and any corresponding variations thereof. The polishing substrates contemplated by the present invention include semiconductor device substrates, such as, silicon, silica, gallium arsenide, silicon nitride, tungsten, tantalum, aluminum, copper, and any other semiconductor device substrate, whether conducting, semi-conducting or insulating.
2. Conditioning. In the art of chemical-mechanical polishing, conventional polishing pads generally must be conditioned or otherwise roughened to initially create, then periodically renew, the pad""s polishing surface. Throughout this specification, xe2x80x9cconditioningxe2x80x9d is intended to mean mechanical and/or chemical surface treatment of a pad""s polishing surface to generate nanoasperities.
3. Nanoasperities. Throughout this specification, xe2x80x9cnanoasperitiesxe2x80x9d are intended to mean:
i. protrusions from the pad surface; and/or
ii. particles which release from the pad surface, having an imputed radius (of curvature) of about 0.5 to about 0.1 microns and sufficient resiliency to permanently deform (measured by the permanent change in curvature during polishing) by less than 25%, more preferably less than 10%.
4. Macro-Defects. Throughout this specification, xe2x80x9cmacro-defectsxe2x80x9d are intended to mean burrs or similar-type protrusions on the pad""s polishing surface of greater than 0.5 microns in any dimension.
5. Particles. For purposes of the present invention, xe2x80x9cparticlexe2x80x9d is intended to mean a discrete mass of material as it exists at the polishing interface. Hence, a xe2x80x9cparticlexe2x80x9d can mean an independent, discrete primary particle, an agglomeration of primary particles which form a discrete mass, and/or primary particles which are aggregated together to form a discrete mass.
6. Self-dressing. Self-dressing is intended to mean that the polishing layer abrades, dissolves, wears or otherwise diminishes during the polishing operation, and as it diminishes, new nanoasperities are formed at the polishing interface, whether the pad is periodically conditioned during its useful life or not.
7. Low modulus phase. xe2x80x9cLow modulus phasexe2x80x9d is intended to mean the portion of the polishing layer which is separate and distinct from the high modulus phase and which defines a modulus of less than about 10 GigaPascals (xe2x80x9cGPaxe2x80x9d).
8. High modulus phase. xe2x80x9cHigh modulus phasexe2x80x9d is intended to mean a portion of the polishing layer which is separate and discrete from the low modulus phase and which defines a modulus greater than about 10 GPa. The high modulus phase may further comprise a particle phase and a non-particle phase.
9. Pre-polymer. xe2x80x9cPre-polymerxe2x80x9d is intended to mean any polymer precursor, including an oligomer, monomer, reactive polymer (including cross-linkable or curable polymers) and/or the like.
During chemical mechanical polishing, abrasive particles are generally intended to be uniformly dispersed in a fluid along the entire polishing interface. Ideally, as new slurry is pumped into the polishing interface (and old slurry moves out of the polishing interface), the abrasive particle distribution remains substantially uniform throughout the polishing interface. With conventional polishing systems, such particle dispersion uniformity (at the polishing interface) is very difficult to achieve, particularly during initial polishing (xe2x80x9cstart-upxe2x80x9d). Non-uniformity of particles at the polishing interface generally lowers polishing efficiency and performance.
Conventional polishing systems generally attempt to improve particle uniformity throughout the polishing interface by flowing large amounts of polishing slurries into the polishing interface and by using slurries with high loadings of abrasive particles. However with such conventional polishing systems, the substrate and polishing equipment generally require extensive cleaning after the polish. This cleaning step slows down production, is prone to operator error and can create environmental concerns.
A need therefore exists in the art for a polishing system which provides improved polishing uniformity along the polishing interface without the need for flowing large amounts of polishing slurries (having high particle loadings) into the polishing interface.
U.S. Pat. No. 5,435,816 to Spurgeon, et al, is directed to an abrasive article having a sheet-like structure for use in abrasion-type polishing of substrates.
The polishing systems of the present invention are directed to the placing of a polishing fluid (which may or may not contain abrasive particles) between a polishing pad and a work-piece to be polished. The pad comprises high modulus and low modulus domains which are exposed at the polishing interface. The work-piece and pad are moved relative to one another, while at least a portion of the polishing fluid is located within the interface between the pad and work-piece. The movement of the pad and/or work-piece and the interaction of the polishing fluid combine to provide (chemical-mechanical) polishing.
Polishing in accordance with the present invention is directed to the removal of surface protrusions by severing the chemical bonds between the protrusion and the surface. This mechanism occurs at a molecular level and is much different from micro-grinding. Micro-grinding occurs on a much larger scale, such as by surface fracturing, cutting or abrading.
Polishing pads in accordance with the present invention comprise a polishing layer created, at least in part, by solidifying a flowable material (including the sintering of flowable solids) into a hydrophilic, polishing layer matrix. Bonded within or onto the polishing layer matrix is a high modulus phase. The low modulus phase of the present invention can be incorporated within or onto the polishing layer matrix and/or can be the polishing layer matrix itself.
The polishing fluid is preferably water based and may also comprise polishing particles (in addition to any particles exposed by or released from the pad). The polishing fluid preferably comprises a pH modifier and optionally a pH buffer, surfactant, chelating agent, and/or oxidizer.
To provide consistency of polishing performance, any polishing pad flow channel(s) should have a configuration whereby as the pad wears to one half the average depth of the largest flow channel, the amount of surface area capable of contacting the substrate changes by less than 30%, more preferably less than 10% and most preferably less than 5%.